Multi-layered laminate structures have long been used to make containers for a variety of products wherein, due to industrial requirements and specifications, it is not possible to use containers made from a single plastic material. In packaging foods, liquids such as various juices, sanitary articles and a host of other products, the container wall must withstand attack by oxygen or some of the ingredients of the packaged product which often tend to permeate through the container wall.
It has, by now, become well known to make multi-layered laminate structures from thermoformable plastics and to make containers therefrom by injection molding or blow molding techniques, and numerous thermoplastic resins have been disclosed and recommended for this purpose. Some of these thermoplastic materials and the composite laminated structures made therefrom are described in U.S. Pat. Nos. 3,560,325; 3,595,740; 3,882,259; 3,955,697; 4,182,457 and 4,234,663, to cite a few.
As mentioned in U.S. Pat. No. 4,234,663, which issued to Catte et al on Nov. 18, 1980, when multi-layer foil structures are used to make containers by thermoforming of the foil, considerable amount of "scrap" is obtained which may be as high as 50% of the total weight of the initially coextruded materials. If the scrap cannot be included in the multi-layered laminate structure, it constitutes a waste which must be disposed of with consequent economic disadvantages.
In their aforementioned patent, Catte et al disclose re-introduction of at least part of the scrap into the multi-layer foil structure as a "supplementary" layer. The scrap-containing layer of Catte et al, however, is constituted by a mixture of the scrap with sufficient amounts of adhesive, which is a graft copolymer of a styrenic monomer on a polyolefinic substrate.
In an article by Muneki Yamada entitled "Oriented Multi-Layer Containers For Food: Solid Phase Pressure Formed Cups and Stretch-Blow Molded Bottles", presented on Mar. 17-19, 1981 at the "5th Annual International Conference On Oriented Plastic Containers", the author discusses the technology of solid phase pressure forming and stretch-blow molding in the manufacture of multi-layer containers. With reference to FIGS. 2 and 3, the author describes a 7-layer structure which comprises a scrap layer interposed between a polypropylene layer and an adhesive layer with no significant reduction in clarity (transparency of the containers) provided the thickness of the scrap layer is within certain critical thickness ratio to the other layers.
At page 5, the Yamada article refers to U.S. Pat. No. 4,182,457 for making "oriented" containers. This patent, however is basically concerned with making transparent containers obtained by orienting the thermoplastic polyolefin olefin layer during stretch blow molding of the parison.
So far as it is known, there is not, at the present, a totally satisfactory method of utilizing all the scrap in making a satisfactory multi-layer laminate for forming containers.
Various apparatus for forming a multi-layered parison and blow molding the parison into a container of the desired shape are known. See, for example, U.S. Pat. Nos. 4,047,868; 4,297,092; 3,802,826; 3,447,204; 3,478,139; 3,546,743; 4,042,661; 4,125,585; 4,134,952; 4,152,104; and 4,281,981. The common features of these apparatus include an annular discharge flow passageway formed between a cylindrical flow tube and a die body, an annular discharge orifice at the downstream end of the annular discharge flow passageway through which the parison or multi-layered laminate structure is extruded, feed passageways which supply resin material to the apparatus for an individual resin layer and connecting passageways which join the feed passageways to the annular discharge flow passageway at junctions where an individual resin layer is added to the multi-layered laminate flowing from upstream of the junction.
In U.S. Pat. No. 4,047,868 the use of pressure rings to control the relative flow of resin material in the connecting passageways and the thickness of the individual layers is taught. Use of annular accumulation chambers to distribute material flowing into the feed passageways circumferentially to form more uniform layers is taught in U.S. Pat. Nos. 4,297,092; 4,152,104; 4,042,661; 3,546,743; 3,478,139; and 3,447,204. Rotation of the die body about the mandrel to provide more uniform layers is described in U.S. Pat. No. 3,802,826. Methods of controlling thickness and concentricity of the layers are taught in U.S. Pat. Nos. 4,047,868; 3,546,743; and 3,446,204.
A principal object of the various apparatus of the several patents mentioned above was to produce multi-layered structures with good roll geometry, that is a gauge thickness of substantially uniform depth across the width. Another object was to provide uniform deposition of a relatively thin molten layer of polymer onto a relatively thick molten layer of polymer under conditions of laminar flow without causing turbulence leading to fusion of the molten layers, uneven laydown of one layer upon the other or aberations which ultimately lead to delaminations when the finished product is subjected to mechanical stress.
These problems become particularly difficult when a relatively thin layer is to be laminated to a relatively thick layer. It is nonetheless important to be able to form laminates including one or more thin layers. For example, a container might be formed with an inner layer, an adhesive layer and an oxygen barrier layer. The inner layer may be formed with a thermoplastic polyolefin, the adhesive layer with a carboxylic acid modified polyolefin and the barrier layer (if oxygen is to be excluded) of a saponified copolymer of ethylene and vinyl acetate. The first mentioned polymers are relatively inexpensive. The last mentioned polymers are specialty chemicals and quite expensive. For economic reasons, therefore, it is important that the expensive polymers be laid down in thin layers. It is equally important for in use performance that the thin layers have good roll geometry, that they completely cover the thick layer and that there be no weak areas subject to delamination under mechanical stress. These ends are difficult to achieve in conventional equipment utilized for the preparation of parisons for blow molding.
It is, accordingly, an object of the present invention to provide a multi-layer laminate structure including a distinct and separate layer of scrap produced from the co-extrudate formed during coextrusion of the different layers of several thermoplastic materials.
It is a further object of this invention to provide a method for efficient and economical utilization of the scrap when making containers from multi-layer laminate structure comprising several thermoplastic materials.
It is also an object of the present invention to make packaging containers from multi-layer laminated structures which include a scrap layer, wherein the container has, inter alia, excellent resistance to oxygen permeability and transparency.
It is a further object of the present invention to provide novel improved apparatus for making a multi-layered parison for blow molding which produces parisons reliably despite variations in the thickness of the layers.
It also an object of this invention to provide an improved apparatus for producing multi-layered structures with layers of uniform thickness and concentricity.